The number of hydrogen atom(s) attached to phosphorus atom in hypophosphorous acid is

  1. zero
  2. one
  3. two
  4. three
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Very pure hydrogen (99.9%) can be made by which of the following processes?

  1. Reaction of salt like hydrides with water
  2. Reaction of methane with steam
  3. Mixing natural hydrocarbons of high molecular weight
  4. Electrolysis of water
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In curing cement plasters, water is sprinkled from time to time. This helps in

  1. keeping it cool
  2. developing interlocking needle ­like crystals of hydrated silicates
  3. hydrating sand and gravel mixed with cement
  4. converting sand into silicic acid
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